the components of the gene delivery vector with charged components (for instance
polyanions such as heparin) is an indicator of the strength of the complexation
(necessary for the extracellular milieu) as well as the possibility of release (in
intracellular milieu, favorable for gene expression).
Testing the efficiency of a polymer in protecting DNA from enzymatic degradation (by nuclease, etc.) gives information about the efficiency of compaction of DNA
by the polycation and/or the steric protection of the polyplex. The protection of DNA
in the polyplex from its degradation by enzymes is essential for in vivo delivery.
1.4 Application in Gene Therapy
One of the many applications of polymers capable of complexing but also condensing DNA is their use as transfection agents (introduce genetic material into cells).
1.4.1 Introduction to Gene Therapy
Gene therapy aims to cure inherited and acquired diseases by correcting the
overexpression or underexpression of defective genes, and its success depends
largely upon the development of vectors that deliver and efficiently express a
therapeutic gene in a specific cell population [85, 86]. Gene therapy protocols
were originally designed to correct inheritable disorders such as adenosine deaminase deficiency, cystic fibrosis, Gaucher’s disease, and Duchenne muscular dystrophy [87, 88]. However, gene therapy is not exclusively used in an attempt to supply
a missing gene product to a patient with a given inborn error of metabolism. Indeed,
gene therapy has been considered more recently as a promising tool for treating
acquired diseases such as cancer [89] and human immunodeficiency virus (HIV)
infections [90]. Clearly, different applications have distinct needs, and tailoring
gene delivery vectors to the specific requirements of a therapeutic application is
still a challenge. For example, the ideal gene vector for treating genetic disorders
should not only deliver intact pDNA efficiently to the nucleus of most of the target
cells, but also, once delivered, the transgene should be maintained in the nucleus
without disrupting host gene expression or signaling pathways. By contrast, anticancer gene therapy trials are in progress in which the aim is high transgene
expression in as many tumor cells as possible, rather than sustained gene expression.
Two types of vectors are used in gene delivery: viral [91] and non-viral
[92, 93]. Viral-mediated DNA vehicles (infection) have played a major role in
gene therapeutics. Unfortunately, the initial enthusiasm associated with the high
infection yields has been tempered by growing concerns regarding safety issues
such as toxicity, immunogenicity, and oncogenicity. On the other hand, synthetic
gene vectors (transfection), with dimensions in the nanometer range, provide potential alternatives for gene therapy because these vectors (based on lipids, dendrimers,
peptides, or polymers) are more easily produced and at lower cost. Moreover, they
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A. Bertin
polyanions such as heparin) is an indicator of the strength of the complexation
(necessary for the extracellular milieu) as well as the possibility of release (in
intracellular milieu, favorable for gene expression).
Testing the efficiency of a polymer in protecting DNA from enzymatic degradation (by nuclease, etc.) gives information about the efficiency of compaction of DNA
by the polycation and/or the steric protection of the polyplex. The protection of DNA
in the polyplex from its degradation by enzymes is essential for in vivo delivery.
1.4 Application in Gene Therapy
One of the many applications of polymers capable of complexing but also condensing DNA is their use as transfection agents (introduce genetic material into cells).
1.4.1 Introduction to Gene Therapy
Gene therapy aims to cure inherited and acquired diseases by correcting the
overexpression or underexpression of defective genes, and its success depends
largely upon the development of vectors that deliver and efficiently express a
therapeutic gene in a specific cell population [85, 86]. Gene therapy protocols
were originally designed to correct inheritable disorders such as adenosine deaminase deficiency, cystic fibrosis, Gaucher’s disease, and Duchenne muscular dystrophy [87, 88]. However, gene therapy is not exclusively used in an attempt to supply
a missing gene product to a patient with a given inborn error of metabolism. Indeed,
gene therapy has been considered more recently as a promising tool for treating
acquired diseases such as cancer [89] and human immunodeficiency virus (HIV)
infections [90]. Clearly, different applications have distinct needs, and tailoring
gene delivery vectors to the specific requirements of a therapeutic application is
still a challenge. For example, the ideal gene vector for treating genetic disorders
should not only deliver intact pDNA efficiently to the nucleus of most of the target
cells, but also, once delivered, the transgene should be maintained in the nucleus
without disrupting host gene expression or signaling pathways. By contrast, anticancer gene therapy trials are in progress in which the aim is high transgene
expression in as many tumor cells as possible, rather than sustained gene expression.
Two types of vectors are used in gene delivery: viral [91] and non-viral
[92, 93]. Viral-mediated DNA vehicles (infection) have played a major role in
gene therapeutics. Unfortunately, the initial enthusiasm associated with the high
infection yields has been tempered by growing concerns regarding safety issues
such as toxicity, immunogenicity, and oncogenicity. On the other hand, synthetic
gene vectors (transfection), with dimensions in the nanometer range, provide potential alternatives for gene therapy because these vectors (based on lipids, dendrimers,
peptides, or polymers) are more easily produced and at lower cost. Moreover, they
126
A. Bertin